5 popular nutritional supplements

The pros and cons of each

Whether to treat symptoms, ward off disease, or just hedge their bets against a less-than-perfect diet, more than 50 percent of U.S. adults have taken nutritional supplements.

But they might expect too much. Initial enthusiasm over certain nutrients can subsequently be dashed by clinical trials showing that supplements have no more effect on health than a placebo, and sometimes even increase the risk of disease.

We reviewed the evidence on five top-selling nutritional supplements, based on 2009 sales data from the Nutrition Business Journal, a trade publication. Here's our advice on each of them.

If you decide to take supplements, look for products with the "USP Verified" mark. That indicates that the U.S. Pharmacopeia, a nonprofit standards-setting authority, has verified the quality, purity, and potency of the raw ingredients or finished product.

Calcium: Don't overdo it

Contrary to some reports suggesting that Americans don't get enough calcium, a review released in November 2010 by the National Academy of Sciences' Institute of Medicine, which helps the government set nutritional recommendations, concluded that most folks actually do. (Girls ages 9 to 18 are the exception.) In fact, the review found that some women older than 50 were in danger of exceeding the new safe upper limit of 2,000 milligrams a day due to widespread use of calcium supplements.

That's a concern because excess calcium might increase the risk of kidney stones. Furthermore, an analysis of 11 studies involving around 12,000 adults suggested an increase in heart-attack risk in those who took calcium supplements. But the analysis excluded people who also took vitamin D, which has been associated with reduced heart-attack risk.

Bottom line

Aim for no more than the recommended daily amounts of calcium: 1,000 mg for most adults, and 1,200 mg for women older than 50 and men older than 70. Three daily servings of calcium-rich foods, such as dairy products, can provide around 900 mg of calcium, plus other beneficial nutrients. Don't take more supplemental calcium than needed to meet your recommended daily intake. And make sure you get adequate vitamin D, which helps you absorb calcium. Check the labels on foods fortified with calcium, such as orange juice, to make sure you don't exceed the daily limits.

Fish oil: Take it to heart

There's good evidence that a higher intake of omega-3 fatty acids from fish or fish-oil supplements can reduce the risk of heart attacks and strokes, and might slow artery hardening in people with existing heart disease. Omega-3s have also been found to reduce joint tenderness from rheumatoid arthritis, and they might elevate mood and help prevent cognitive decline, eye disease, and some cancers.

Bottom line

People who have heart disease or rheumatoid arthritis should aim for 1 gram daily of DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) combined, an amount that usually requires several fish-oil capsules. Everyone else should try to eat two or more servings of fatty fish a week (pick low-mercury ones like herring and wild salmon). It's unclear whether the ALA (alphalinolenic acid) form of omega-3s in flaxseed and some vegetable oils provides the same health benefits. And since the body has to convert ALA to the other forms, you need more servings to get a meaningful amount.

Glucosamine and chondroitin: Possibly helpful

Research is mixed on whether these supplements can slow the progression of osteoarthritis. But there's some decent evidence that they can alleviate pain in a subset of patients with moderate to severe arthritis of the knee based on a large, multicenter trial published in 2006.

Bottom line

People with arthritis pain might consider taking 1,500 mg of glucosamine sulfate and 1,200 mg of chondroitin sulfate daily, separated into three doses. Stop after three months if you don't see improvement in your pain severity. Talk with your doctor before taking glucosamine if you have a shellfish allergy, since it's made from the shells of sea creatures. And don't take glucosamine with warfarin (Coumadin and generic) because it can interfere with the blood-thinning action of the drug.

CoQ10: Some early promise

There's some evidence, though by no means definitive, that this vitamin-like compound, also called ubiquinone, might help prevent migraine headaches, slow the progression of Parkinson's disease, ease the effects of muscular dystrophy, and possibly lower blood pressure. When taken along with other medications, CoQ10 might ease the symptoms of congestive heart failure.

Some preliminary evidence suggests that it might also reduce the muscle aches that statin drugs can cause. But there's not yet enough research to recommend CoQ10 for that purpose.

Bottom line

CoQ10 might be helpful for people with the conditions listed above. There's no recommended daily intake for it, but doses for most indications have ranged from 100 mg to 300 mg daily (divided into two or three doses). Because CoQ10 might lower blood pressure, talk with your doctor before taking it if you take blood-pressure medication.

Magnesium: An overlooked mineral

Magnesium improves calcium absorption to help bolster bones and protects the heart against abnormal heart rhythms and blood clots. It also helps control blood sugar. Several large studies have found that people who consume the most magnesium are less likely to develop type 2 diabetes or a crucial contributing factor called insulin resistance. For people with diabetes, some evidence suggests that magnesium supplements might help with long-term blood sugar control.

Bottom line

Most people can meet their daily magnesium needs by eating a variety of fiber-rich foods, such as legumes, nuts (especially almonds), whole grains, and green, leafy vegetables. But nutritional surveys suggest that some older adults don't meet their recommended daily intake of 320 mg for women and 420 mg for men. They should talk with their doctor about having their magnesium level checked via a simple blood test, and about taking a supplement if the level is too low. Those with poorly controlled diabetes or those who take medication that can deplete magnesium, including certain antibiotics, cancer drugs, and diuretics, should also discuss supplements with their doctor.

Don't take magnesium supplements on your own, since many people, especially older adults, have undiagnosed kidney disease. That could cause a dangerous buildup of the mineral in the body. Finally, note that many antacids and laxatives contain magnesium.